Type I sum of squares are also called sequential sum of squares because they are considered successively, so the order that you enter terms in the model (i.e., list of Effects in Fit Model launch dialog) is important. They are not the default test in JMP. They are obtained from the platform menu with the Sequential Tests command.
Type II sum of squares are not available in JMP.
Type III sum of squares is the default test in Fit Least Squares. They represent the additional sum of squares attributed to the given term. They are not dependent on the order of the terms.
As Jim advised, you can find more information by searching or in any applied regression textbook.